Swimming-induced pulmonary edema (SIPE) symptoms last more than 2 days in 38% of cases and recur within 30 months in 28% of cases during open-water swimming. These are among study finding published in Chest.

Researchers in Sweden assessed individuals with respiratory symptoms indicative of SIPE from 2017-2019 following a large, open-water swimming event. Telephone interviews were conducted with these individuals at 10 days and 30 months, and individuals not reached by phone received the questionnaire by mail. Participants were asked about continuing symptoms, symptom duration, experiences of respiratory symptoms while swimming in open water after SIPE, need for medical evaluation after SIPE, and frequency of physical activities (endurance, strength, and swimming exercise) during the previous 12 months.

Of the 26,125 individuals (aged ≥18 years; 53% female) who participated in the swimming event, 246 participants had been assessed for respiratory symptoms and 165 (mean [SD] age, 48 [10] years; 90% female) were diagnosed with SIPE. The 10-day follow-up was conducted in 132 participants and the 30-month follow-up in 152 participants.

Dyspnea (81%) and cough (82%) were the most common acute respiratory symptoms reported at the swimming event’s mobile medical unit (MMU). At the 10-day follow-up, 112 (85%) individuals reported symptoms that continued after leaving the MMU, which lasted more than 2 days for 50 individuals (38%) and more than 5 days for 28 individuals (21%). Asthma was associated with a symptom duration of more than 2 days (odds ratio [OR], 2.56; P =.045), after adjustment for age and hypertension.

The present large cohort study challenges the established hallmark of SIPE duration of <48 hours, while the recurrence of SIPE was within the previously reported range.

At 30 months, 23 patients (15%) reported symptoms that had continued for more than 10 days, and 6 patients (4%) reported continuing symptoms after 12 months. Dyspnea, cough, and reduced fitness were the most common continuing symptoms reported in the 2 follow-up interviews.

At 30 months, 64 patients had swum in open water again, of whom 18 patients (28%) reported episodes of respiratory symptoms while swimming. Asthma was associated with recurrence of SIPE at the 30-month follow-up (OR, 6.91; P =.022), after adjustment for age and hypertension. Among the participants with recurrence of SIPE, 28% (5/18) had asthma vs 7% (3/46) in individuals without recurrence.

About 90% of participants at the 30-month follow-up reported that their self-assessed general health (90%) and level of physical activity (69%) were not affected by SIPE. In a comparison of their subjective health status before and after SIPE, 93% reported an equal or improved self-assessed general health, and 85% reported an equal or higher physical activity level. In addition, 88 individuals (58%) stated that they never swam in open water again after their diagnosis of SIPE.

Limitations include the small number of SIPE cases and a shift in diagnostic criteria during the study period. Also, recall and self-reporting bias are possible, and the questionnaire was not thoroughly validated.

“The present large cohort study challenges the established hallmark of SIPE duration of <48 hours, while the recurrence of SIPE was within the previously reported range,” stated the study authors. “These results provide valuable information on short- and long-term outcomes for swimmers, swim-event organizers, and health care professionals.”

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